In this time of shortages, high purity carbon may be added to the lengthening list of raw materials which are now in short supply. This situation is readily evident to foundries and other consumers who have watched the price of metallurgical grade carbon, which is an essential ingredient in the production of iron, practically double within the last year. For the consumer who cannot justify the large capital expense of the known carbon purification processes, this situation presents serious economic problems.
In addition to these problems related to metallurgical grade carbon, it is noteworthy that this country depends largely on foreign sources for the high purity natural graphite which is used in many lubrication and electrical applications. This situation may be a source of future problems to several American industries.
Several methods have been developed to purify carbon. For example, U.S. Pat. No. 3,501,272 describes a method which uses mineral acids to remove unwanted impurities, primarily ash. The process described in U.S. Pat. No. 2,657,118 describes a high temperature method using chlorine gas to remove impurities in coke, and U.S. Pat. No. 2,624,698 uses "volatilizable fluorides" at a temperature of at least 250.degree.C. to purify the coke. However, each of these processes, while effective, involves the use of corrosive materials at high temperatures. Extreme care is required in handling these materials and in protecting equipment and the environment against their corrosive effect.